CMOS switching circuitry of a transmitter module
Transmit modules typically constitute passive matching circuitry, harmonic trap filters and an antenna switch to provide isolation between the transmit bands as well as between transmit and receive functions. In complementary metal-oxide semiconductor (CMOS) processes the switch function is difficult to implement as a large voltage swing may result in breakdown of the MOS oxide, drain diode, source diode as well as substrate diodes. Therefore a switching function is provided at a node that has low impedance during transmit that limits the voltage swing that the MOS switches experience. The approach is particularly useful, but not limited to, half duplex transmissions such as those used in global system for mobile (GSM) communication, enhanced data for GSM Evolution (EDGE), and time division synchronous code division multiple access (TDSCDMA).
1. An apparatus comprising:
a first signal path for a first frequency band comprising a first power amplifier (PA) a first matching circuit and a first filtering circuit;
a second signal path for a second frequency band, the second frequency band being different from the first frequency band; and
a first switching circuit coupled to the second signal path to enable routing of a second signal from the second signal path to an antenna coupled to the apparatus such that at least a transmit switch of the first switching circuit is not subject to a transmit voltage swing.
2. The apparatus of claim 1 , wherein the second signal path further comprises a second power amplifier (PA), a second matching circuit an input of which is coupled to an output of the second PA, and a second filtering circuit an input of which is coupled to an output of the second matching circuit.
3. The apparatus of claim 1 , wherein the first switching circuit further comprises a shunt switch that is closed during transmit of a signal to an antenna and open during receipt of a signal from an antenna.
4. The apparatus of claim 3 , wherein the shunt switch is coupled to the second signal path by means of a passive network.
5. The apparatus of claim 4 , wherein the passive network comprises at least one of: a capacitor, an inductor, a network comprising at least a capacitor and at least an inductor.
6. The apparatus of claim 1 , wherein the first switching circuit further comprises a series switch that is open during transmit of a signal to an antenna and closed during receipt of a signal from an antenna.
7. The apparatus of claim 1 , further comprising:
a second switching circuit coupled to the first signal path to enable routing of a first signal from the first signal path to an antenna such that at least a transmit switch of the second switching circuit is not subject to a transmit voltage swing; and
a diplexing filter coupled to an output of the first and second signal paths, an output of the diplexing filter coupled to an antenna.
8. The apparatus of claim 7 , wherein the second signal path further comprises a second PA, a second matching circuit an input of which is coupled to an output of the second PA, and a second filtering circuit an input of which is coupled to an output of the second matching circuit.
9. A circuit in a transmit module comprising:
a passive network comprising a first node and a second node, the first node connected to an output of a signal path of the transmit module;
a shunt switch having a first pole connected to the second node of the passive network and a second pole connected to ground; and
a series switch having a first pole connected to the first pole of the shunt switch;
wherein when the transmit module is in transmit mode the shunt switch is closed and the series switch is open.
10. The circuit of claim 9 , wherein the passive network comprises at least one of: a capacitor, an inductor, a network comprising at least a capacitor and at least an inductor.
11. The circuit of claim 9 , wherein when the transmit module is not in transmit mode the shunt switch is open and the series switch is closed.